http://math.bu.edu/people/levit/AlbertEinstein.pdfJohn Stachel: "Albert Einstein: A Man for the Millenium? (...) It was Albert Einstein (Zur Elektrodynamik bewegter Körper, 1905) who first realized the need to replace such ideas, based on classical kinematics, with a new kinematics based on four key ideas: 1. Omit all reference to the hypothetical ether frame; 2. Take the failure of all attempts to detect absolute motion at face value, and postulate the relativity principle (all inertial frame of reference are equivalent) for all physical phenomena; 3. Add the WELL-TESTED postulate that the speed of light is independent of that of its source; 4. Combining 1, 2 and 3, one can derive the Lorentz transformations between any two inertial frames of reference."

John Stachel knows perfectly well that the postulate that the speed of light is independent of that of its source was by no means WELL-TESTED. Rather, in 1887 the Michelson-Morley experiment UNEQUIVOCALLY confirmed the variable speed of light predicted by Newton's emission theory of light:

http://www.philoscience.unibe.ch/documents/kursarchiv/SS07/Norton.pdfJohn Norton: "These efforts were long misled by an exaggeration of the importance of one experiment, the Michelson-Morley experiment, even though Einstein later had trouble recalling if he even knew of the experiment prior to his 1905 paper. This one experiment, in isolation, has little force. Its null result happened to be fully compatible with Newton's own emission theory of light. Located in the context of late 19th century electrodynamics when ether-based, wave theories of light predominated, however, it presented a serious problem that exercised the greatest theoretician of the day."

http://philsci-archive.pitt.edu/1743/2/Norton.pdfJohn Norton: "In addition to his work as editor of the Einstein papers in finding source material, Stachel assembled the many small clues that reveal Einstein's serious consideration of an emission theory of light; and he gave us the crucial insight that Einstein regarded the Michelson-Morley experiment as evidence for the principle of relativity, whereas later writers almost universally use it as support for the light postulate of special relativity. Even today, this point needs emphasis. The Michelson-Morley experiment is fully compatible with an emission theory of light that CONTRADICTS THE LIGHT POSTULATE."